1. Field of the Invention
The present invention relates to an information processing apparatus, a data processing apparatus, and methods thereof and, more particularly, to a technique of protecting the right of a holder of data stored in a storage medium.
2. Description of the Related Art
The rapid growth and spread of computers and networks is promoting digitization of a variety of information such as text data, image data, and audio data and distribution of these digital data. However, distribution of digital data via a wide area network such as the Internet is fraught with danger of eavesdropping or wiretapping on the transmission path by third parties. Not only data on a transmission path but also digital data stored in a storage medium is not safe because an unauthorized third party who has no access right may copy and illicitly use and leak it. It is common practice to encrypt digital data in order to ensure a safe transmission path or securely store data in a portable storage medium.
It is easy to copy, edit, and modify digital data. The ability to copy, edit, and modify with ease is useful for users but simultaneously induces the necessity to protect digital data against illicit alteration by third parties. There are digital signatures and a message authentication code (MAC), which add anti-alteration data to verify the presence/absence of alteration of digital data. A digital signature has not only an alteration verification function but also a function of preventing spoofing and repudiation.
Cryptography to implement the above-described mechanisms will be described below.
[Hash Function]
A hash function is used together with a digital signature process to shorten the process time of signature addition by lossy-compressing data to be signed. That is, a hash function has a function of processing data M with an arbitrary length to generate output data with a predetermined length. An output H(M) of the hash function is called a hash value for the plaintext data M.
Particularly, a one-way hash function that is given the data M cannot practically be used to calculate plaintext data M′ satisfying H(M′)=H(M) due to amount of calculation. Examples of the one-way hash function are MD2 (Message Digest 2), MD5 (Message Digest 2), and SHA-1 (Secure Hash Algorithm 1).
[Public Key Cryptosystem]
As a characteristic feature of a public key cryptosystem using two different keys, data encrypted by one of the keys can be decrypted by only the other key. One of the two keys is called a public key and can be open to the public. The other key is called a private key and is held by only an authorized person. With this characteristic feature, one key (public key) can be open to the public. Hence, transmission of the key is easy because it is unnecessary to give it to a communication partner secretly. Examples of the public key cryptosystem are RSA encryption and ElGamal encryption.
[Digital Signatures]
Examples of digital signatures using a public key cryptosystem are an RSA signature, DSA signature, and Schnorr signature.
[Message Authentication Code]
A digital signature is a message authentication system that guarantees the right of a document creator by using a public key cryptosystem. Another message authentication system using a common key cryptosystem or a hash function instead of a public key cryptosystem is called a message authentication code (MAC).
The MAC is largely different from a digital signature in that a sender (MAC value creator) and a recipient (authenticator) share secret data (key K in keyed-hashing for message authentication code (HMAC)). It is advantageous because the amount of calculation is smaller than a digital signature. However, since the authenticator also holds the secret data, it is impossible for a third party to prove the creator of MAC, that is, sender or recipient. The MAC using a standard hash function such as SHA-1 is used for a security protocol such as IPSec (IP Security protocol) or SSL (Secure Socket Layer) in a network.
[Image Data Protection in Digital Camera]
Using the above-described cryptography or digital signatures enables protection of image data taken by a digital camera from threats such as eavesdropping or wiretapping, alteration, and spoofing.
A technique described in Japanese Patent Laid-Open No. 2005-18914 aims at protecting data recorded in a portable storage medium and implements copy protection and data encryption. More specifically, a data recording program and a data reproduction program, which can be activated by a computer, are written in a portable storage medium in advance. That is, there exists a technique of imparting a copyright protecting function to a portable storage medium.
Contents containing image data are not always distributed by using portable storage media. In another method, contents are freely distributed via a network. A technique described in Japanese Patent Laid-Open No. 2004-118327 causes a specific server administrator to control utilization of contents acquired via, for example, a network. That is, there exists a copyright protection technique of causing a device to communicate with a server and obtain a permission to use a content, assuming that the device to use the content connects to a network.
Normally, a photographer, who is a content creator, can freely delete or transfer image data he/she has taken by using, for example, a digital camera. However, a photographer is not always a holder of rights in the contents (i.e., the content owner). For example, a content owner may be is a publishing company, while a photographer is a cameraman who has a contract with the company. In this case, the photographer may transfer captured image data to third parties (other than the contracting party) erroneously or intentionally. To prevent this, it is necessary to establish a mechanism for causing an entity (content owner) different from the photographer to protect the copyright of image data.
The technique of Japanese Patent Laid-Open No. 2005-18914 encrypts image data by using special storage media. This method is disadvantageous in two points: the purchase cost of special storage media and the unusableness of existing storage media. The technique of Japanese Patent Laid-Open No. 2004-118327 requires network connection to use contents. This is not always convenient for content users.
To set right protection in a camera on a remote site, it is necessary to bring the camera from the site to the place where the content owner is. To avoid this, a demand has arisen for a mechanism that registers a memory card for a camera in a remote site as a medium capable of right protection, thereby protecting image data stored in the memory card upon shooting.